Modern architecture and passive solar design both call for increased use of glazing in structures. Although advances have been achieved in the insulating properties of walls and ceilings, windows remain comparatively poor insulators.
The current state of the art in window design uses multiple glazed windows in which two or three panes of glazing contain an entrapped air space, or spaces. The intervening air, or sometimes other gas, is used as an insulator. Although significantly better than single pane windows, these multiple glazed windows are still relatively poor insulators.
Heat is lost through double glazed windows in three ways, conduction, convection and radiation. The inside pane of a double glazed window in a heated structure absorbs heat from it's surroundings. Some of this heat is conducted directly through the air between the panes, to the outside pane. When the space between the panes is greater than 3/8 of an inch convection currents occur between the panes. The air tends to move in circular fashion, absorbing heat from the inner pane and delivering it to the outer pane.
These two methods of heat loss are common knowledge to anyone possessing ordinary skill in the art. It might appear obvious to such a person of only ordinary skill, that the insulating properties of a window could be greatly enhanced by removing the air between the panes, and thus eliminating the loss of heat resulting from conduction and convection. However, a little bit of knowledge can be a dangerous thing. This conclusion rests on the assumption that the amount of heat transmitted by radiation remains constant. Detailed experimentation and testing by this applicant has revealed that this assumption is incorrect and that when the air is removed from between the panes of a double glazed window, the amount of heat transmitted through the window is not reduced but actually doubled. Further detailed experimentation and testing by this applicant has revealed the means by which this surprising result occurs quite contrary to the result which was assumed would be the obvious effect by those possessing only ordinary skill and knowledge.
The inner warmer pane of the window emits long wave infra-red radiations which travel toward the colder outside pane. When the intervening space between the panes contains air, approximately two thirds of these radiations are absorbed by the air and the heat is thereafter slowly conducted and convected to the outer pane, actually intercepting the high speed radiations. When the air is removed however, and there is therefor no absorption medium, the long wave infra red radiations, which travel at the speed of light, rapidly transmit heat from the inner pane to the outer pane at a greatly accelerated rate transmitting an even greater amount of heat than that saved by the elimination of conduction and convection and resulting in a total heat transfer twice as large as that occurring through the an evacuated window.
Stanley et al. in U.S. Pat. No. 4,357,187 entitled WINDOW OVERLAY FOR THERMAL INSULATION, made the apparently obvious but incorrect assumption that evacuating the window to any degree would increase insulating effectiveness. Clearly Stanley et al did not properly test their assumption or they would have learned that what seemed obvious to them was in practise incorrect and produces the opposite and undesirable result. Stanley et al have proposed their invention as an energy conserving means. However, actual implementation of their proposed invention results in increased energy loss. This put in serious question, the validity of the Stanley et al patent as it is clearly not "USEFULL".
In any event, teachings and conclusions, which are scientifically and experimentally untrue can hardly be cited as valid prior art.